The present invention is directed to a device for conveying a plate-like sheet, such as sheets of paper board or corrugated board, within a rotary multi-color printing machine for plate-like matter or sheets.
In practical use, machines, which include a feeding station and several printing units allowing a production of a multi-color print and, if necessary, a cutting station, a stripping station and final station for the delivery of the sheets, must be able to handle sheets having important dimension up to a length of 5 meters and a width of 3 meters. The use of such a machine involves the compulsory accessibility to the inner space of the printing unit, whether it is either for changing the printing plates on the plate cylinder, for providing various settings of the inking process, or for cleaning the distributor and inking rollers.
For achieving the operation mentioned above, most machines presently built are fitted on lengthwise extending rails. This allows a disconnection of the links between two successive printing units and the shifting of the units, either upstream or downstream, on the rails to provide a space between two adjacent units which allows access to these units. With certain machine designs, it is possible to pull the printing unit laterally from the whole assembly and, thus, provide access and the possibility of easy working on the rollers. Such solutions, particularly those of shifting the printing units, might become inadequate on larger machines on account of the number of links that need to be disconnected, as well as the weight of the various printing units.
For large machines or installations, the designers have preferred to provide a permanent free space and to add a sheet conveyance device between the printing units. Obviously such a conveying device is expected to be adjustable to the width and thickness of the board or sheets being conveyed. The device used up to now consists of a horizontal frame holding a row of striated shafts extending orthogonally with regard to sheet travelling direction. With this system, two lateral beams are to hold the carrier rollers arranged opposite striated shaft. These two lateral beams are held symmetrically for the sidewise functions, as defined with regard to the lengthwise axis of the machine. Such lateral beams are held by two crosswise shafts, one which is destined to hold the vertical position of the lateral beams and the other to drive the carrier rollers. Sidewise shifting of the lateral beams is insured by threaded axles acting as pairs on both lateral beams. In this way, the actuation of the threaded axles allows the lateral beams to be moved together or apart in such a way that the carrier rollers are moved to a position as required, for instance on the non-printed edges of the sheets or with the possibilities permitting to any other area enabling the conveyance without the hazard of mackling the print. Moreover, the vertical position of the upper frame carrying the striated shafts can be adjusted in such a way as to provide between the shafts and their respective rollers the distance required by the sheet thickness.
The above-described device has numerous drawbacks. In fact, as may easily be understood, the two lateral edges or the area on which the carrier rollers and the striated shafts act should be conspicuously free from print as otherwise the sheets conveyed might be mackled.
If the sheet is carried on its printed edge, mackling will occur. To avoid this, it is appropriate to increase the sheet width in such a way as to obtain transportation on the print-free area. However, this entails unwanted waste.
Another or second drawback involved with this type of arrangement is that the edges or any other area originating from the compulsory sheet pinching which depends on the board features is likely to result in leaving the sheet with imprints, which are unacceptable on the final product to be manufactured from the printed sheets.
A third drawback is that the arrangement involves fastidious settings of the device with regard to width and thickness of the sheets. In fact, on the one hand, it is easy to conceive motorized sidewise shifting of the lateral beams but, on the other hand, vertical setting of the cradle can be achieved mechanically with sufficient precision only by means of considerable backlash on the cams, pinions and levers. As with any setting, several tries are necessary with subsequent correction before a satisfactory result can be obtained. Even after such settings have been carefully obtained, subsequent adjustments, both in the lengthwise and sidewise settings with certain sheets are likely to occur in the course of a production run. Finally, and especially so, this device necessitates a voluminous mechanism causing the cost to increase and limiting access to the upper part of the printing unit, particularly at the contact level between the impression cylinder and the printing plate cylinder.